The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro Complications — Understanding Costs and UK Access
Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist injection for weight management. While clinical trials showed promising results, understanding potential complications, costs, and how to access it safely in the UK is essential. Whether you're considering NHS or private routes, this guide explains what you need to know about complications, pricing, and eligibility. Always consult your GP before starting any weight loss medication.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Mounjaro Complications and What to Expect
Mounjaro can cause side effects ranging from mild to serious. Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — these often improve as your body adjusts. Common effects include indigestion, acid reflux, fatigue, dizziness, injection site reactions, and hair loss. Most side effects are temporary, but individual responses vary significantly.
Serious complications are rare but require urgent medical attention: severe, persistent stomach pain spreading to the back (possible pancreatitis), gallbladder problems, serious allergic reactions, or vision changes in people with diabetes. Some users experience gastroparesis (stomach paralysis) symptoms. Others report decreased appetite beyond the intended effect, leading to inadequate nutrition if not monitored.
- Nausea typically peaks in the first weeks and often reduces with continued use
- Dose titration (gradual increase) helps minimise gastrointestinal complications
- Oral contraceptives may be less effective — add barrier methods for 4 weeks after starting and after each dose increase
- Mounjaro vs Wegovy: both are GLP-1 agonists but Mounjaro's dual mechanism may cause different side effect profiles
Contact your GP immediately if you experience severe abdominal pain, persistent vomiting, signs of pancreatitis, or allergic reactions.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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Mounjaro Cost and UK Access Routes
Private prescription costs in the UK typically range from £129 to £320 per month, depending on your dose. Lower starting doses (2.5 mg) cost less; maximum doses (15 mg) cost more. You'll also need an online consultation with a UK-licensed prescriber (usually £20–£50), though some providers include this in package pricing. Each KwikPen contains 4 weekly doses, so calculate your monthly cost based on your current dose tier.
NHS access is through tier 3 specialist weight management services — not standard GP prescription. You'll need referral from your GP, clinical assessment, and acceptance into your regional ICB service. NHS waiting lists vary from weeks to over a year depending on your area. Eligibility requires BMI ≥30 (or ≥27.5 with weight-related comorbidities for South Asian backgrounds). Use our free BMI calculator to check your starting point, then discuss NHS or private routes with your GP.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
What are the most common complications of Mounjaro?
Nausea, diarrhoea, vomiting, and constipation are very common, especially during the first weeks. These typically improve as your body adjusts. Indigestion, fatigue, and injection site reactions are also common. Serious complications like pancreatitis are rare but require urgent medical attention if severe abdominal pain occurs.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs range from approximately £129–£320 per month depending on your dose. Starting doses (2.5 mg) are cheaper; maximum doses (15 mg) cost more. Add £20–£50 for an initial online consultation. Prices vary by provider, so compare options before committing.
Can I get Mounjaro on the NHS in the UK?
Yes, but access is through specialist tier 3 weight management services, not standard GP prescription. You'll need referral and clinical assessment. Eligibility requires BMI ≥30 (or lower thresholds for certain ethnic backgrounds). NHS availability and waiting lists vary significantly by region — ask your GP about local services.
What's the difference between Mounjaro and Wegovy in terms of complications?
Both are GLP-1 agonists causing similar common side effects. Mounjaro is a dual GIP and GLP-1 agonist, so it may cause a slightly different side effect profile. Mounjaro's additional GIP mechanism may provide more appetite suppression but can also cause different gastrointestinal effects. Individual responses vary; your prescriber will help choose what suits you.
How do I get a Mounjaro prescription online in the UK?
You'll need to find a GPhC-registered online pharmacy or prescribing service. You'll complete an online health questionnaire, have a consultation with a UK-licensed prescriber (often via video call), and receive a prescription if approved. They'll assess your BMI, health history, and eligibility. Never buy Mounjaro without a valid UK prescription.
Ready to take control of your weight loss journey?
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